Reagent concentration, temperature, and residence time are known factors that drive chemical reactions. Combustion chemical vapor deposition (combustion CVD) processes are no different. The significance of these factors and their controlling process parameters has been well documented.
Combustion chemical vapor deposition (combustion CVD) is a relatively new technique for the growth of coatings. Combustion CVD is described, for example, in U.S. Pat. Nos. 5,652,021; 5,858,465; and 6,013,318, each of which is hereby incorporated herein by reference in its entirety.
Conventionally, in combustion CVD, precursors are dissolved in a flammable solvent and the solution is delivered to the burner where it is ignited to give a flame. Such precursors may be vapor or liquid and fed to a self-sustaining flame or used as the fuel source. A substrate is then passed under the flame to deposit a coating.
There are several advantages of combustion CVD over traditional pyrolytic deposition techniques (such as CVD, spray and sol-gel, etc.). One advantage is that the energy required for the deposition is provided by the flame. A benefit of this feature is that the substrate typically does not need to be heated to temperatures required to activate the conversion of the precursor to the deposited material (e.g., a metal oxide). Also, a curing step (typically required for spray and sol-gel techniques) typically is not required. Another advantage is that combustion CVD techniques do not necessarily require volatile precursors. If a solution of the precursor can be atomized/nebulized sufficiently (e.g., to produce droplets and/or particles of sufficiently small size), the atomized solution will behave essentially as a gas and can be transferred to the flame without requiring an appreciable vapor pressure from the precursor of interest.
Conventional combustion CVD processes involve passing a precursor material directly through the entire length of the flame. In some conventional techniques, a precursor/solvent solution is used as the fuel source. The temperature and residence time profile experienced by the precursor is controlled by the combustion conditions and/or burner-to-substrate distance. Unfortunately, however, these control mechanisms can be fairly limited, depending on the particular application.
The inventor of the instant application has realized that independent control over precursor delivery within a self-sustaining flame would provide greater reaction control capability and, to this end, has developed the burner design of certain example embodiments that enhances control. Additionally, confining the precursor reaction zone within a relatively small portion of the combustion reaction zone should provide a more consistent product, e.g., by substantially narrowing the distribution of the time/temperature profile experienced by the precursor.
The vast majority of combustion deposition work performed to-date by the assignee of the instant application has used a linear burner developed by Webber and provided by SURA Instruments. FIG. 1 is a simplified view of an apparatus 100 including a linear burner used to carry out combustion deposition. A combustion gas 102 (e.g., a propane air combustion gas) is fed into the apparatus 100, as is a suitable precursor 104 (e.g., via insertion mechanism 106, examples of which are discussed in greater detail below). Precursor nebulization (108) and at least partial precursor evaporation (110) occur within the apparatus 100 and also may occur external to the apparatus 100, as well. The precursor could also have been delivered as a vapor reducing or even eliminating the need for nebulization The flame 18 may be thought of as including multiple areas. Such areas correspond to chemical reaction area 112 (e.g., where reduction, oxidation, and/or the like may occur), nucleation area 114, coagulation area 116, and agglomeration area 118. Of course, it will be appreciated that such example areas are not discrete and that one or more of the above processes may begin, continue, and/or end throughout one or more of the other areas.
Particulate matter begins forming within the flame 18 and moves downward towards the surface 26 of the substrate 22 to be coated, resulting in film growth 120. As will be appreciated from FIG. 1, the combusted material comprises non-vaporized material (e.g., particulate matter), which is also at least partially in particulate form when coming into contact with the substrate 22. To deposit the coating, the substrate 22 may be moved (e.g., in the direction of the velocity vector). Of course, it will be appreciated that the present invention is not limited to any particular velocity vector, and that other example embodiments may involve the use of multiple apparatuses 100 for coating different portions of the substrate 22, may involve moving a single apparatus 100 while keeping the substrate in a fixed position, etc. The burner 110 is about 5-50 mm from the surface 26 of the substrate 22 to be coated.
The linear burner shown in FIG. 1 may be fueled by a premixed combustion gas comprising propane and air. It is, of course, possible to use other combustion gases such as, for example, natural gas, butane, etc. The standard operating window for the linear burner involves air flow rates of between about 150 and 300 standard liters per minute (SLM), using air-to-propane ratios of about 15 to 25. Successful coatings require controlling the burner-to-lite distance to between about 5-50 mm when this particular burner is used.
As one example of how this particular burner was used, it is noted the inventor of the instant application attempted to deposit a single layer anti-reflective (SLAR) film of silicon oxide (e.g., SiO2 or other suitable stoichiometry) on a glass substrate to alter the optical and other properties of the glass substrates (e.g., to increase visible transmission). The attempt achieved an increase in light transmission in the visible spectrum (e.g., wavelengths of from about 400-700 nm) over clear float glass with an application of the film on one or both sides of a glass substrate. In addition, increases in light transmission for wavelengths greater the 700 nm are also achievable and also may be desirable for certain product applications, such as, for example, photovoltaic solar cells. The clear float glass used in connection with the description herein is a low-iron glass known as “Extra Clear,” which has a visible transmission typically in the range of 90.3% to about 91.0%. Of course, the examples described herein are not limited to this particular type of glass, or any glass with this particular visible transmission. More particularly, using the above techniques, the inventor of the instant application was able to produce coatings that provided a transmission gain of 1.96% or 1.96 percentage points over the visible spectrum when coated on a single side of clear float glass. The transmission gain may be attributable in part to some combination of surface roughness increases and air incorporation in the film that yields a lower effective index of refraction. Typical process conditions for successful films used a burner air flow of about 225 SLM, an air-to-propane ratio of about 19, a burner-to-lite distance of 35 mm, and a glass substrate velocity of about 50 mm/sec.
Recently, efforts have focused on investigating alternative burner designs. These efforts have led to the exploration of infrared and non-linear (e.g., two dimensional) burners produced by Maxon Corporation. One example of an IR burner design is disclosed in co-pending and commonly assigned application Ser. No. 12/000,784, filed on Dec. 17, 2007, the entire contents of which is hereby incorporated herein by reference.
Some techniques use a combustion deposition device in which the precursor is delivered independent of the flame. This approach is described in, for example, U.S. Publication No. 2005/0061036, the entire contents of which is hereby incorporated herein by reference. However, these products appear to involve substantially different burner designs and also appear to be limited to the deposition of optical preforms. Current remote CCVD (R-CCVD) efforts, such as those performed by Innovent, for example, aim for greater control over reaction conditions by delivering the precursor externally to the flame. The assignee of the instant invention currently is working with Innovent (Jena, Germany) to develop a remote combustion CVD technology for the deposition of titanium oxide coatings. In one example of such a process, the precursor is delivered to the substrate between two burners. The proposed design of certain example embodiments (described in greater detail below) differs from R-CCVD efforts in that the precursor may be passed directly through a predetermined portion of the flame where combustion is taking place, although this is not a requirement of the design. In certain example embodiments that also differ from R-CCVD efforts, the precursor may be sent substantially directly into a given location of the reaction (combustion) zone from within the flame. Additionally, the part of the flame through which the precursor passes can be adjusted, which provides different temperature and residence time profiles and different concentrations and types of various reactive species in the flame. The precursor may be substantially entirely enclosed in the combustion reaction zone in certain example embodiments.
In view of the above, although certain conventional and/or current techniques provide some control over the above-noted and/or other factors, further improvements are still possible and desired. Indeed, the inventor of the instant application is not aware of any commercially available burners that have been developed specifically for combustion deposition techniques. Thus, it will be appreciated that there is a need in the art for a burner system that provides enhanced control over reagent concentration, temperature, residence time, and/or other factors. It also will be appreciated that there is a need in the art for a versatile burner capable of accommodating large area combustion deposition coating applications.
In certain example embodiments of this invention, a burner for use in combustion deposition depositing a coating on a substrate is provided. First and second spaced-apart combustion gas manifolds are configured to respectively produce first and second flames (which may effectively combine to form a single flame front beyond the outer face of the burner in certain example embodiments). The first and second combustion gas manifolds form a precursor reaction zone therebetween. An adjustable precursor delivery manifold located between the first and second combustion gas manifolds is configured to receive a precursor used in forming the coating. The precursor delivery manifold is positioned so as to substantially directly provide the precursor to a desired or predetermined portion of the precursor reaction zone, which may be within the flame. The precursor delivery manifold includes first and second cooled walls arranged to reduce the occurrence of precursor pre-reactions upstream of the precursor reaction zone.
In certain example embodiments, a combustion deposition burner is provided. First and second spaced-apart combustion gas manifolds are configured to respectively produce first and second flames (which may effectively combine to form a single flame front beyond the outer face of the burner in certain example embodiments). The first and second combustion gas manifolds form a precursor reaction zone therebetween. A vertically adjustable precursor delivery manifold located between the first and second combustion gas manifolds is configured to receive a precursor. The precursor delivery manifold is positioned so as to substantially directly provide the precursor to a desired or predetermined portion of the precursor reaction zone, and is at least partially defined by first and second cooled walls arranged to reduce the occurrence of precursor pre-reactions upstream of the precursor reaction zone. At least one capillary system is provided to receive a cooling heat transfer oil or other suitable heat transfer fluid. First and second ceramic refractories surround the first and second cooled walls. Each said combustion gas manifold includes a plurality of bleed holes and at least one baffle arranged to provide a substantially uniform gas flow across a face thereof. The precursor delivery manifold is configured to provide to the combustion reaction zone a substantially uniform distribution of a carrier that includes the precursor.
In certain example embodiments, a method of forming a coating on a glass substrate is provided. A burner having first and second spaced-apart combustion gas manifolds is configured to respectively produce first and second flames (which may effectively combine to form a single flame front beyond the outer face of the burner in certain example embodiments). A precursor reaction zone is formed between the first and second flames. A precursor used in forming the coating is provided substantially directly to a desired or predetermined portion of the precursor reaction zone via a vertically adjustable precursor delivery manifold located between the first and second combustion gas manifolds. The precursor delivery manifold includes first and second cooled walls arranged to reduce the occurrence of precursor pre-reactions upstream of the precursor reaction zone.
In certain example embodiments, a method of making a coated article comprising a coating supported by a substrate is provided. A burner having first and second spaced-apart combustion gas manifolds is configured to respectively produce first and second flames. A precursor reaction zone is formed between the first and second flames. A precursor used in forming the coating is provided substantially directly to a desired or predetermined portion of the precursor reaction zone via a vertically adjustable precursor delivery manifold located between the first and second combustion gas manifolds. The precursor delivery manifold includes first and second cooled walls arranged to reduce the occurrence of precursor pre-reactions upstream of the precursor reaction zone.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.